We don't control our heart – it's an involuntary muscle – but special pacemaker cells help keep it ticking away.

Montreal Alouettes quarterback Johnny Manziel is tackled by the Ottawa Redblacks in Ottawa on Aug. 11, 2018. Manziel was subsequently placed under the CFL concussion protocol.
(THE CANADIAN PRESS/Justin Tang)
August 19, 2018

One bout of exercise protects your heart immediately, and the effect lasts for several days.

This 119 million year old fish, Rhacolepis, is the first fossil to show a 3D preserved heart which gives us a rare window into the early evolution of one of our body’s most important organs.
Dr John Maisey, American Museum of Natural History in New York
April 19, 2016